In recent years, rapid progress has been made in the spread of BS (Broadcast Satellite) and CS (Communication Satellite) digital broadcasting, or terrestrial digital broadcasting, and many devices equipped with a digital broadcast reception function are available, including digital TVs, recorders, and portable terminals. Channel switching processing during digital broadcast reception performed by such digital broadcast reception apparatuses requires control information that is inserted periodically into a signal transmitted from a broadcasting station. The wait time for receiving this data causes lengthening of a time period during which display is not possible.
In channel switching processing during digital broadcast reception, program identification information (PAT (Program Association Table) and PMT (Program Map Table)) reception processing, ECM (Entitlement Control Message) reception processing, and sequence header reception processing, are essential. This processing causes lengthening of a time period during which display is not possible (a time period during which preparatory processing for displaying selected channel video is performed after channel switching occurs).
A PAT and PMT are sent from a broadcasting station in approximately 100 msec unit cycles. PAT and PMT acquisition processing is performed at random timing unrelated to this sending cycle, and therefore a reception wait time of up to 100 msec occurs.
As with a PAT and PMT, an ECM is also sent from a broadcasting station in approximately 100 msec unit cycles. Here, too, ECM acquisition processing is performed at random timing unrelated to this sending cycle, and therefore a reception wait time of up to 100 msec occurs.
A reception wait time also occurs in sequence header reception processing. Data compressed by means of MPEG2 (Moving Picture Expert Group 2) encoding is composed of a GOP (Group Of Pictures) in which a plurality of pictures are grouped, there being three types of picture—I-picture, P-picture, and B-picture. An I-picture can be decoded by itself, a P-picture is a picture obtained by encoding a difference from a past picture, and a B-picture is obtained by encoding differences from data predicted from both past and future pictures.
A sequence header is placed immediately before an I-picture placed at the start of a GOP, and contains resolution (1920×1080, 1440×1080, etc.) and aspect ratio (16:9, 4:3) information as video information for a selected channel. Decoding processing at the time of channel switching processing can only start after this sequence header has been received and video information has been acquired. This sequence header is sent from a broadcasting station in approximately 500 msec unit cycles. Sequence header acquisition processing is performed at random timing unrelated to this sending cycle, and therefore a reception wait time of up to 500 msec occurs.
As described above, in a digital broadcast reception apparatus, program identification information (PAT (Program Association Table) and PMT (Program Map Table)) reception processing, ECM (Entitlement Control Message) reception processing, and sequence header reception processing, are essential in channel switching processing during digital broadcast reception. This processing causes lengthening of a time period during which display is not possible (a time period during which preparatory processing for displaying selected channel video is performed after channel switching occurs).
In Patent Literature 1, a method is disclosed whereby video data decoding processing is performed using cached program identification information intended to reduce wait time that occurs in program identification information reception processing. With the method described in Patent Literature 1, the use of cached program identification information makes hitherto executed program identification information acquisition processing unnecessary, and makes it possible to shorten a time period during which display is not possible that occurs at the time of channel switching.